Assessment of Metal Chelators in Wort- and Beer-Simulating Buffer Solutions

Tuur Mertens
Technical University of Berlin

Keywords: Metal chelation, ROS

Flavor stability remains one of the most challenging quality aspects in brewing. Transition metals (iron, copper and manganese) constitute in beer staling and oxidation, as they catalyze the Fenton and Haber-Weiss reactions in the formation of reactive oxygen species (ROS).

Chelating them whilst brewing could potentially reduce deterioration of beer freshness and ultimately prolong shelf-life. In this study, 10 compounds were selected and screened for their complexing capacities with 8 metal ions (Fe3+, Fe2+, Ca2+, Zn2+, Mg2+, Mn2+, Cu2+, Cu+, and an all-including mix) in both a wort- and beer-simulating acetate buffer solution.

Measurements were done by UV/VIS and ICP-OES spectroscopy, respectively, to assess changes in absorption; and monitor reductions in metal concentration after incubation and filtration (0,45 and 0,2 µm). Ideal chelators bind iron, copper and manganese in a way that they can no longer participate in the generation of ROS, without removing metals that are vital for the yeast and the brewing process.

At the time of writing, the results (partial and ongoing) suggest gallotannin, gallic acid, and tannic acid to be selective chelators for iron and copper. Manganese, unfortunately, is not readily complexed.